VCE Biology Question Thread

[MM1]

Why do T cells mature in the thymus gland? Thanks!

[nerdmmb]

Why do T cells mature in the thymus gland? Thanks!

I'm going to have a go..

There are different types of T cells so the thymus gland aids the maturation of T cells into specific types such as T-helper cells or T-cytotoxic cells.

[vox nihili]

Why do T cells mature in the thymus gland? Thanks!

Thymus glands will contain the chemical mix that allow haempoetic cells to differentiate into T-cells. Otherwise, you can't really separate out those chemicals and get different types of cells.

[MM1]

Thymus glands will contain the chemical mix that allow haempoetic cells to differentiate into T-cells. Otherwise, you can't really separate out those chemicals and get different types of cells.

Thanks! Can the same be said with B cell lymphocytes?

Also do we need to know about all the types of immunoglobulins?

[vox nihili]

Thanks! Can the same be said with B cell lymphocytes?

Also do we need to know about all the types of immunoglobulins?

Pretty much. It's just so that you can expose them to an environment that will allow them to differentiate that way. Just so you can sort out the pieces etc.

Nope

[alchemy]

I'm now confused with a rather substantial concept or idea in the biology course - differentiating the feedback mechanisms.
So far, I'm aware that negative feedback is achieved when the stimulus response mechanism acts to reduce the effect of the original stimulus. And a positive feedback mechanism acts to increase the effect of the original stimulus. I've also read that positive feedback mechanisms are relatively rare because they impose a certain degree of instability to body mechanisms.

However, the real difficulty I'm having is in distinguishing both of them in certain cases (especially using diagrams). For example, in the attached image, the answers to that question (un-attached) indicate both 'inhibition of the hypothalamus' and 'stimulation of the anterior pituitary gland' as negative feedback mechanisms. However, how can these be negative feedback mechanisms by performing the opposite actions? If thyroxine is at a low level, and if the anterior pituitary is stimulated to produce TSH, shouldn't that be a typical example of positive feedback?

[grannysmith]

Are second messengers considered effectors in signal transduction?

[alchemy]

Are second messengers considered effectors in signal transduction?

Nope, even their name suggests they're the opposite (messengers effectors). Second messengers activate a seperate "secondary effector" which activates transcription factors to produce a protein product in response to the stimulus.

[nhmn0301]

I'm now confused with a rather substantial concept or idea in the biology course - differentiating the feedback mechanisms.
So far, I'm aware that negative feedback is achieved when the stimulus response mechanism acts to reduce the effect of the original stimulus. And a positive feedback mechanism acts to increase the effect of the original stimulus. I've also read that positive feedback mechanisms are relatively rare because they impose a certain degree of instability to body mechanisms.

However, the real difficulty I'm having is in distinguishing both of them in certain cases (especially using diagrams). For example, in the attached image, the answers to that question (un-attached) indicate both 'inhibition of the hypothalamus' and 'stimulation of the anterior pituitary gland' as negative feedback mechanisms. However, how can these be negative feedback mechanisms by performing the opposite actions? If thyroxine is at a low level, and if the anterior pituitary is stimulated to produce TSH, shouldn't that be a typical example of positive feedback?

If I have LOW LEVEL of thyroxine, which is not sufficient to stimulate metabolism and growth, that can influence on the body function right? Hence, we need to keep the amount of thyroxine at a relatively constant amount, in this case, if I have TOO LITTLE thyroxin, I need to raise the amount of hormones that I have by stimulate the anterior pituitary gland, which in turn stimulate TSH, to produce MORE thyroxin. Hence, in the end, we have the initial stimulus as LOW LEVEL of thyroxin, and the response as RAISING THE LEVEL of thyroxin. Isn't that negative feedback mechanism, which negates the initial stimulus?

Yeah I know positive and negative feedback can be a bit annoying sometimes, I think it's just a matter of which side are you considering. I am always confused with the bleeding stimulus of the body. For example, if I take it as a negative feedback mechanism, the body will obviously try to prevent the blood loss as much as possible by constricting the arterioles. But if I take it as a positive feedback mechanism, I can explain it because the body will try to stop the amount of bleeding by actually releasing more blood, which carries platelets and fibrin, factors that can produce clotting.

[katie101]

When people inadvertently put their hands in very hot water, they feel the heat before they feel the pain. Both signals are transmitted to the brain by nerves. Do the nerves appear to have the same speed of conduction? Explain.

Thanks guys!

[nhmn0301]

When people inadvertently put their hands in very hot water, they feel the heat before they feel the pain. Both signals are transmitted to the brain by nerves. Do the nerves appear to have the same speed of conduction? Explain.

Thanks guys!

Nerves don't have the same speed as conduction, because the longer you leave your hand in the hot water, every single second goes by, more tissues will be destroyed, hence, the signal needs to be extremely fast to prevent the damages. Whilst heat conduction, it just simply let you realise that you are placing your hand in hot water, nothing more, the sooner or longer you feel that heat, it doesn't matter, it won't help you from getting less tissue damage. What matters here is the speed of the response the body need to carry to minimise as much damage as possible. Hence, you actually pull your hand away from the hot water before you even feel the heat.

[alchemy]

Can somebody please explain an instance of when a positive feedback mechanism decreases the stability of a biological system in an organism?

[MM1]

Can somebody please explain an instance of when a positive feedback mechanism decreases the stability of a biological system in an organism?

The birth process perhaps? As a woman is in labour, the pituitary gland releases the hormone oxytocin which stimulated muscles in the uterus to contract. With the release of many other hormones, a hormonal imbalance occurs and this often results in conditions such as post-natal depression.
Someone please correct me if I'm wrong.

[vox nihili]

The birth process perhaps? As a woman is in labour, the pituitary gland releases the hormone oxytocin which stimulated muscles in the uterus to contract. With the release of many other hormones, a hormonal imbalance occurs and this often results in conditions such as post-natal depression.
Someone please correct me if I'm wrong.

Sounds good to me

[RazzMeTazz]

How many electrons and hydrogen ions join with the acceptor molecule NADP+ to form NADPH?

Is it two electrons and one hydrogen ion?